Really, really interesting link from Slashdot - Command Line is your friend, in which a bunch of complete newbies are shown through a linux CLI.
"The command line is one-dimensional with a single point of concentration: the cursor. The vertical axis of the screen is always time and provides the newbie with a constant reminder of what they did along with a record to show their instructor when they have problems."
"she progressed rapidly in remembering the command names now pronouncing commands like 'mkdir' as 'muk-dear' as opposed to 'em-kay-dee-eye-ah'." (I remember doing this ;)
"It was explained to the users that computers were stupid and would only do as you told them. They understood a special restricted form of language "as if you were talking to a child"."
"One user grasped the concept rather early on and usefully described it to the others as "a box with other boxes in"." (Re file structures)
"All users preferred the bash notification to the alert box style used in GUIs."